Take Shelter," about a small-town Ohio family man racked by ominous nightmares, begins frighteningly and gets progressively more so. What starts out as a kind of apocalyptic horror fantasy gradually morphs into a more psychological realm – which makes the horror even more unsettling. The bogeyman in this film is inside, not outside.

Curtis (Michael Shannon) would seem to have it all: a good job as the crew manager for a drilling company; a beautiful, adoring wife, Samantha (Jessica Chastain); and a 6-year-old daughter, Hannah (Tova Stewart), who, though severely hearing-impaired, is seemingly happy and well adjusted.

But Curtis can't dispel the nightmares that increasingly crowd in on him. He imagines storm clouds massing in the sky, tornadoes bearing down on his family, huge flocks of blackbirds. Even in his waking moments, on the job, he is hit by sudden frightful visions. Acting obsessively on his fears, and to everyone's befuddlement, he constructs a much-expanded storm shelter in his backyard by taking out a risky home loan and illegally borrowing company equipment.

This is especially heart-wrenching because Curtis, who is only trying to protect his family, is an inarticulate man who can't really fathom what is happening to him. He has an abiding suspicion that he has inherited his mother's schizophrenia. In one of the film's most moving sequences, where he visits her in the assisted-living facility where she has been for decades, he tries to find out from her if the onset of her condition matches his own. Kathy Baker, as the mother, is only in this one scene, but it's so beautifully played that it resonates throughout the rest of the film like a soft, plaintive chord.

Writer-director Jeff Nichols, whose previous film "Shotgun Stories" also starred Shannon, has the rare ability to think big and work small. His new film is both allegorical and intimate, with a suggestiveness that goes way beyond its spare story line. Curtis's free-floating anxieties are intended to connect up with our fears about the collapsing economy, about the safety of the world and our families, but Nichols never loses sight of the small-scale human dramas at the film's core

On one level, for example, despite all its apocalyptic trappings, "Take Shelter" is a fierce portrait of a marriage in dissolution. But it's also a portrait of how two good people fight to keep their happiness when faced with something neither of them fully comprehends. Chastain doesn't soften Samantha's predicament. We can see how aghast this woman is at what her husband has become. He's a stranger – and yet she feels closer to him than to anybody.

Curtis is especially caring with his daughter, who seems to be the calm in the eye of his storm. She grounds his sanity. But Curtis's fears that he may be going crazy tear him (and us) apart. Since this would represent only another form of madness, it is no solace at all to him that he alone may foresee Armageddon.

Shannon understands, as few actors do, how madness and the fear of losing control are not pretexts for acting-class histrionics. Many of his best effects are extraordinarily subtle. He acts with an intuitive understanding of how terror can freeze you up. When Curtis does unleash his demons, as in a scene where he explodes during a Lions Club potluck dinner, the effect is beyond harrowing because he is ripping himself apart and he can't help himself – and he knows it.

A few faults: By trying to expand Curtis's anxieties into a universal state of free-floating dread, Nichols somewhat overplays his hand. He's a bit too fond of symbolism – why does he make the daughter deaf? – and this has the effect of flattening out the fears. The doomy special effects are borderline tacky. Also, the ending, which I won't reveal, is ambiguous in all the wrong ways and cheats what came before. It's easy enough to blot out, though, since the rest of the movie is so good. Grade: A- (Rated R for some language.)